Conventionally, in chemical plants, and the like, positioners are provided for regulator valves that are used in flow rate processes, where the openings of the regulator valves are controlled by the positioners. A positioner is provided with a calculating portion for calculating a deviation between an opening setting value, which is sent from a higher-level device, and the actual opening that is fed back from the regulator valve, to generate, as a control output, a control signal that is dependent on that deviation, an electropneumatic converting device for converting the control output that is generated by the calculating portion into a pneumatic pressure signal, and a pilot relay for amplifying the pneumatic pressure signal, converted by the electropneumatic converting device, and outputting it to an operating device of the regulator valve as an amplified pneumatic pressure signal. See, for example, Japanese Unexamined Utility Model Registration Application Publication S62-28118.
FIG. 6 illustrates the flow of input/output signals in a control valve structured from a positioner and a regulator valve. In this figure, 100 is the positioner, 200 is the regulator valve, and 300 is the control valve that is structured from the positioner 100 and the regulator valve 200, where the positioner 100 is provided with an electric module 1, an EPM (an electropneumatic converting module) 2, and a pilot relay (a pneumatic pressure amplifying module) 3.
The electric module 1 inputs an opening setting signal Iin and a signal (the valve opening signal) Pv that indicates the actual opening X of a valve, fed back from the regulator valve 200, to produce, as a control output, an EPM driving signal (a PWM signal (duty signal)) Mv. The EPM 2 inputs the EPM driving signal Mv from the electric module 1, and converts this EPM driving signal Mv into a nozzle back pressure Pn. The pilot relay 3 inputs the nozzle back pressure Pn from the EPM 2, to produce the operating device pressure Po from the nozzle back pressure Pn. The regulator valve 200 inputs the operating device pressure Po from the positioner 100, to regulate the opening X of the valve depending on the operating device pressure Po.
In such a control valve 300, the positioner 100 has an auto tuning function, and, for example, automatically obtains the gain of the input/output characteristics of the control valve 300 in order to determine the control parameter. For example, in the positioner disclosed in Japanese Patent 4244507, as illustrated in FIG. 7, the initial value Mv(0) for the EPM driving signal Mv is outputted and a check is performed as to whether or not the valve opening signal Pv(0) is in the operating range, the EPM driving signal Mv(1) is outputted and the valve opening signal Pv(1) is obtained, following which the EPM driving signal Mv(2) is outputted and the valve opening signal Pv(2) is obtained, and the input/output characteristic gain of the control valve is calculated from the amount of change between the EPM drive signals Mv(1) and Mv(2) and the amount of change between the valve opening signals Pv(1) and Pv(2). In this case, the EPM drive signals Mv are changed in the same direction, that is, the opening of the valve is changed in the same direction, and thus the input/output characteristic gain is calculated with the hysteresis canceled out.
However, in the method illustrated in FIG. 7, it is not possible to calculate all at once parameters such as input/output characteristic hysteresis and intercept, and the like, through the single action of calculating the gain for the input/output characteristics. FIG. 8 illustrates the relationship between the EPM driving signal Mv and the valve opening signal Pv (that is, the input/output characteristics) when the regulator valve is caused to undergo reciprocating motion. In these input/output characteristics, H indicates a hysteresis and C indicates the intercept.
Note that hysteresis is used when determining control parameters (referencing, for example, Japanese Patent 3511458), and used as a parameter in fault evaluations. In Japanese Unexamined Patent Application Publication 2003-308101, for example, the hysteresis is used in a comparison with the frictional force at the time of proper operation. The intercept can be used as a parameter when calculating a fluid reactive force.
The present invention was created in order to solve such problems, and an aspect of the present invention is to provide a parameter acquiring device and method wherein it is possible to calculate all at once other parameters, such as hysteresis and the intercept, in a single operation of calculating the gain of the input/output characteristics.